Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound

---

Query: EC:3.4.25.1 (proteasome)
28,817 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Temporal control of p27(Kip1) (p27) degradation imposes periodicity in its activity during cell cycle progression and its accumulation during cell cycle exit. Degradation of p27 is initiated by phosphorylation of p27 at Thr-187, which marks the protein for ubiquitination by SCF(Skp2) and subsequent proteolysis by the 26S proteasome. Here we show that the p27 ubiquitination activity in cell extracts depends on the presence of the ubiquitin-like protein Nedd8 and enzymes that catalyze Nedd8 conjugation to proteins. Moreover, we show that reconstitution of the p27 ubiquitination activity of recombinant SCF(Skp2) also requires Nedd8 conjugation pathway components. Inactivation of the Nedd8 conjugation pathway by a dominant negative mutant of the Nedd8-conjugating enzyme Nce1/Ubc12 blocks the ubiquitination and degradation of p27 in cell extracts. Consistent with a role in cell-cycle progression, Nedd8 is expressed in proliferating cells and is itself down-regulated upon cellular differentiation. These results suggest that the Nedd8 conjugation pathway may regulate the turnover of p27(Kip1), independently of p27 phosphorylation, and further establishes the identity of protein components involved in p27 ubiquitination. Finally, these findings provide a direct demonstration of a function for Nedd8 in a biological process.
...
PMID:A Nedd8 conjugation pathway is essential for proteolytic targeting of p27Kip1 by ubiquitination. 1078 Oct 63

The ubiquitin-proteasome pathway plays an important role in control of the abundance of cell cycle regulators. Mice lacking Skp2, an F-box protein and substrate recognition component of an Skp1-Cullin-F-box protein (SCF) ubiquitin ligase, were generated. Although Skp2(-/-) animals are viable, cells in the mutant mice contain markedly enlarged nuclei with polyploidy and multiple centrosomes, and show a reduced growth rate and increased apoptosis. Skp2(-/-) cells also exhibit increased accumulation of both cyclin E and p27(Kip1). The elimination of cyclin E during S and G(2) phases is impaired in Skp2(-/-) cells, resulting in loss of cyclin E periodicity. Biochemical studies showed that Skp2 interacts specifically with cyclin E and thereby promotes its ubiquitylation and degradation both in vivo and in vitro. These results suggest that specific degradation of cyclin E and p27(Kip1) is mediated by the SCF(Skp2) ubiquitin ligase complex, and that Skp2 may control chromosome replication and centrosome duplication by determining the abundance of cell cycle regulators.
...
PMID:Targeted disruption of Skp2 results in accumulation of cyclin E and p27(Kip1), polyploidy and centrosome overduplication. 1079 Mar 73

F-box proteins are critical components of the SCF ubiquitin-protein ligase complex and are involved in substrate recognition and recruitment for ubiquitination and consequent degradation by the proteasome. We have isolated cDNAs encoding a further 10 mammalian F-box proteins. Five of them (FBL3 to FBL7) share structural similarities with Skp2 and contain C-terminal leucine-rich repeats. The other 5 proteins have different putative protein-protein interaction motifs. Specifically, FBS and FBWD4 proteins contain Sec7 and WD40-repeat domains, respectively. The C-terminal region of FBA shares similarity with bacterial protein ApaG while FBG2 shows homology with the F-box protein NFB42. The marked differences in F-box gene expression in human tissues suggest their distinct role in ubiquitin-dependent protein degradation.
...
PMID:cDNA cloning and expression analysis of new members of the mammalian F-box protein family. 1094 68

The ubiquitin protein ligase SCF(Skp2) is composed of Skp1, Cul1, Roc1/Rbx1 and the F-box protein Skp2, the substrate-recognition subunit. Levels of Skp2 decrease as cells exit the cell cycle and increase as cells re-enter the cycle. Ectopic expression of Skp2 in quiescent fibroblasts causes mitogen-independent S-phase entry. Hence, mechanisms must exist for limiting Skp2 protein expression during the G(0)/G(1) phases. Here we show that Skp2 is degraded by the proteasome in G(0)/G(1) and is stabilized when cells re-enter the cell cycle. Rapid degradation of Skp2 in quiescent cells depends on Skp2 sequences that contribute to Cul1 binding and interference with endogenous Cul1 function in serum-deprived cells induces Skp2 expression. Furthermore, recombinant Cul1-Roc1/Rbx1-Skp1 complexes can catalyse Skp2 ubiquitylation in vitro. These results suggest that degradation of Skp2 in G(0)/G(1) is mediated, at least in part, by an autocatalytic mechanism involving a Skp2-bound Cul1-based core ubiquitin ligase and imply a role for this mechanism in the suppression of SCF(Skp2) ubiquitin protein ligase function during the G(0)/G(1) phases of the cell cycle.
...
PMID:The F-box protein Skp2 is a ubiquitylation target of a Cul1-based core ubiquitin ligase complex: evidence for a role of Cul1 in the suppression of Skp2 expression in quiescent fibroblasts. 1103 4

The transition from G1 phase to S phase of the mammalian cell cycle is controlled by many positive and negative regulators, among which cyclin E and p27Kip1, respectively, undergo the most marked changes in concentration at this transition. The abundance of both cyclin E and p27Kip1 is regulated predominantly by posttranslational mechanisms, in particular by proteolysis mediated by the ubiquitin-proteasome pathway. Cyclin E and p27Kip1 each bind to and undergo polyubiquitination by the same ubiquitin ligase, known as SCF(Skp2). The degradation of cyclin E and p27Kip1 is greatly impaired in Skp2-deficient mice, resulting in intracellular accumulation of these proteins. In this article, recent progress in characterization of the molecular mechanisms that control the proteolysis of cyclin E and p27Kip1 is reviewed.
...
PMID:Regulation of the cell cycle at the G1-S transition by proteolysis of cyclin E and p27Kip1. 1135 28

Targeting of the cyclin-dependent kinase inhibitor p27(Kip1) for proteolysis has been thought to be mediated by Skp2, the F-box protein component of an SCF ubiquitin ligase complex. Degradation of p27(Kip1) at the G(0)-G(1) transition of the cell cycle has now been shown to proceed normally in Skp2(-/-) lymphocytes, whereas p27(Kip1) proteolysis during S-G(2) phases is impaired in these Skp2-deficient cells. Degradation of p27(Kip1) at the G(0)-G(1) transition was blocked by lactacystin, a specific proteasome inhibitor, suggesting that it is mediated by the ubiquitin-proteasome pathway. The first cell cycle of stimulated Skp2(-/-) lymphocytes appeared normal, but the second cycle was markedly inhibited, presumably as a result of p27(Kip1) accumulation during S-G(2) phases of the first cell cycle. Polyubiquitination of p27(Kip1) in the nucleus is dependent on Skp2 and phosphorylation of p27(Kip1) on threonine 187. However, polyubiquitination activity was also detected in the cytoplasm of Skp2(-/-) cells, even with a threonine 187 --> alanine mutant of p27(Kip1) as substrate. These results suggest that a polyubiquitination activity in the cytoplasm contributes to the early phase of p27(Kip1) degradation in a Skp2-independent manner, thereby promoting cell cycle progression from G(0) to G(1).
...
PMID:Degradation of p27(Kip1) at the G(0)-G(1) transition mediated by a Skp2-independent ubiquitination pathway. 1168 78

Eukaryotic cells possess overlapping mechanisms to ensure that DNA replication is restricted to the S phase of the cell cycle. The levels of hOrc1p, the largest subunit of the human origin recognition complex, vary during the cell division cycle. In rapidly proliferating cells, hOrc1p is expressed and targeted to chromatin as cells exit mitosis and prereplicative complexes are formed. Later, as cyclin A accumulates and cells enter S phase, hOrc1p is ubiquitinated on chromatin and then degraded. hOrc1p destruction occurs through the proteasome and is signaled in part by the SCF(Skp2) ubiquitin-ligase complex. Other hORC subunits are stable throughout the cell cycle. The regulation of hOrc1p may be an important mechanism in maintaining the ploidy in human cells.
...
PMID:Human origin recognition complex large subunit is degraded by ubiquitin-mediated proteolysis after initiation of DNA replication. 1193 57

GATA-2 is considered to be essential for the development, maintenance, and function of hematopoietic stem cells (HSCs). However, it was also reported that GATA-2 inhibits the growth of HSCs. To examine the role of GATA-2 in the growth of hematopoietic cells, we introduced an estradiol-inducible form of GATA-2 (GATA-2/estrogen receptor [ER]) into interleukin 3 (IL-3)-dependent cell lines, Ba/F3, 32D, and FDC-P1. Estradiol-induced GATA-2 suppressed c-myc mRNA expression and inhibited IL-3-dependent growth in these clones. As for this mechanism, GATA-2 was found to inhibit ubiquitin/proteasome-dependent degradation of p21(WAF1) and p27(Kip1) and to induce their accumulation by repressing the expression of Skp2 and Cul1, both of which are components of the ubiquitin ligase for p21(WAF1) and p27(Kip1). Overexpression of c-myc restored the expression of Skp2 and Cul1 mRNA, reduced the amounts of p21(WAF1) and p27(Kip1) proteins, and canceled GATA-2-induced growth suppression, suggesting that down-regulation of c-myc expression may be primarily responsible for GATA-2-induced growth suppression. Next, we transduced retrovirus containing GATA-2/ER into murine bone marrow mononuclear cells (MNCs) and stem/progenitor (Sca-1(+)Lin(-)) cells. GATA-2/ER suppressed cytokine-dependent growth of MNCs and Sca-1(+)Lin(-) cells by about 70%, which was also accompanied by the reduced expression of c-myc, Skp2, and Cul1 mRNA and the accumulation of p21(WAF1) and p27(Kip1) proteins. In addition, the amount of GATA-2 protein was found to decline in hematopoietic stem/progenitor cells that were promoted to enter cell cycle by the stimulation with cytokines. These results suggest that GATA-2 may regulate expression levels of p21(WAF1) and p27(Kip1), thereby contributing to the quiescence of hematopoietic stem/progenitor cells.
...
PMID:GATA-2/estrogen receptor chimera regulates cytokine-dependent growth of hematopoietic cells through accumulation of p21(WAF1) and p27(Kip1) proteins. 1239 44

PAX3-FKHR is an oncogenic form of the developmental regulator Pax3 transcription factor. PAX3-FKHR results from a t(2,13) chromosomal translocation, a unique genetic marker of alveolar rhabdomyosarcoma. In this study, we showed that ectopic expression of PAX3-FKHR, but not Pax3, in fibroblasts altered cell cycle control and accelerated G(0)/G(1) to S cell cycle transition. PAX3-FKHR-expressing cells had reduced expression of p27(Kip1) protein, a key cell cycle regulator. The reduction in p27(Kip1) levels by PAX3-FKHR resulted from destabilization of p27(Kip1) as shown by cycloheximide treatment and in vivo pulse-chase labeling experiments. The reduced p27(Kip1) protein level in PAX3-FKHR-expressing cells was restored to the level of control cells by treatment with chemical inhibitors that specifically blocked 26 S proteasome activity. Along with the reduction in p27(Kip1) protein, PAX3-FKHR-expressing cells exhibited elevated expression of F-box Skp2 protein, a substrate-specific component of SCF (Skp1-Cullin-F box protein) ligase involved in the cell cycle-dependent control of p27(Kip1) ubiquitination and 26 S proteasome dependent degradation. Finally, we showed that ectopic expression of p27(Kip1) in PAX3-FKHR-expressing cells significantly reduced the proliferation and colony-forming potential of these cells, implicating that down-regulation of p27(Kip1) protein played an active role in the PAX3-FKHR-directed cell transformation.
...
PMID:PAX3-FKHR transformation increases 26 S proteasome-dependent degradation of p27Kip1, a potential role for elevated Skp2 expression. 1240 4

Disruption of the gene for the cyclin dependent kinase inhibitor (CDKI) p27/kip1 results in pituitary corticotroph hyperplasia while diminished expression of this protein has been described in aggressive human pituitary tumors. We have previously shown that 1,25-vitamin D3 (VD) hypophosphorylates p27 and interferes with the degradation of this CDKI in thyroid carcinoma cells. In this study we investigated whether VD/EB1089 can induce p27 accumulation and cause growth arrest of pituitary corticotroph cells. VD and EB1089 exhibited a significant reduction in AtT20 corticotroph but not PRL235 lactotroph cell growth. These changes were accompanied by selective accumulation of p27 in AtT20 but not in PRL235 cells. As p27 levels are highly dependent on protein degradation, we examined the effect of VD/EB1089 on p27 association with factors that target this CDKI to the proteasome. VD/EB1089 significantly restricted the association of p27 with Skp2 as well as with cyclin dependent kinase 2 (CDK2). As the tumor suppressor and phosphatase PTEN has been implicated in p27 regulation, we tested whether the effects of VD/EB1089 on p27 accumulation in corticotrophs could be mediated through this pathway. VD/EB1089 did not appreciably alter PTEN expression. Moreover, transfection of PTEN did not influence the effect of VD on p27 accumulation in corticotrophs. We conclude that VD/EB1089 can selectively arrest pituitary corticotroph growth and induce p27 accumulation.This effect is mediated at least partially through diminished p27 association with Skp2 and with CDK2. In contrast to other cell systems, PTEN does not participate in the regulation of corticotroph p27 and is not involved in mediating the effect of VD on p27 in these cells. Our findings highlight p27 and VD analogs as targets for manipulation and drug development respectively in the treatment of inoperable corticotroph adenomas.
...
PMID:Vitamin D and its analog EB1089 induce p27 accumulation and diminish association of p27 with Skp2 independent of PTEN in pituitary corticotroph cells. 1240 27


1 2 3 4 5 6 7 8 9 10 Next >>

---